If I was an automotive engineer, I'd be rubbing my hands together in glee with the changes that now in place.
Going through the document again, so much of the modifed car scene is affected. eg:
Camshaft Changes
Diff Ratio Changes
Carby Changes
Old School stuff like 9 inch diff installs
Most people do these things one at a time, and if the certification process costs say $700 a go, then its going to get expensive. People will most likely have to make all the changes in one hit to keep the costs down.
However, I feel that this is a good thing really as a lot of crap cars are going to have to be made safe. Plus we'll probably see a lot more certifiers available and products that a ADR compliant out of the box.
The downside is that things are going to be more expensive